The main value of Reflection is that it can be used to inspect assemblies, types, and members. It's a very powerful tool for determining the contents of an unknown assembly or object and can be used in a wide variety of cases.
Opponents of Reflection will cite that it is slow, which is true when compared to static code execution--however Reflection is used throughout the .NET framework, and provided that it's not abused it can be a very powerful tool in the toolkit.
Some useful applications:
Determining dependencies of an assembly
Location types which conform to an interface, derive from a base / abstract class, and searching for members by attributes
(Smelly) testing - If you depend on a class which is untestable (ie it doesn't allow you to easily build a fake) you can use Reflection to inject fake values within the class--it's not pretty, and not recommended, but it can be a handy tool in a bind.
Debugging - dumping out a list of the loaded assemblies, their references, current methods, etc...
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